Orthodromic Atrioventricular Reentry Bradycardia and Tachycardia Caused by an Accessory Pathway in Horses.
Authors: Buschmann Eva, Easton-Jones Charlotte, Van Steenkiste Glenn, De Wilde Hans, Roberts Veronica, Durando Mary, Decloedt Annelies, Marr Celia, van Loon Gunther
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Accessory pathways—abnormal muscular connections that bypass the normal atrioventricular node-His-Purkinje conduction system—have long been recognised as a cause of arrhythmia in humans and small animals, yet their occurrence in equine patients remains virtually undocumented in the veterinary literature. Buschmann and colleagues present the first comprehensive equine case series of orthodromic atrioventricular reentry tachycardia (OAVRT) and associated bradycardia precipitated by accessory pathway conduction, establishing that this mechanism operates in horses much as it does in other species. The team employed multi-lead electrocardiography, electrophysiological testing, and imaging techniques to characterise the arrhythmia mechanism across multiple affected animals, demonstrating that retrograde conduction through an accessory pathway creates a reentry circuit capable of generating both tachycardic episodes and rate-limiting bradycardia. These findings carry significant clinical weight: equine practitioners should now consider accessory pathway-mediated arrhythmias in differential diagnoses of unexplained tachycardia or bradycardia, particularly in younger horses or those presenting with episodic arrhythmias refractory to conventional antiarrhythmic therapy. Recognition of this condition may prompt earlier referral for specialist electrophysiological evaluation and consideration of catheter ablation, a therapeutic option that has proven effective in affected animals.
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Practical Takeaways
- •Equine clinicians should be aware that accessory pathways are a differential diagnosis for unexplained cardiac arrhythmias in horses, particularly when preexcitation patterns are noted on ECG
- •OAVRT should be considered in horses presenting with recurrent tachycardia or bradycardia episodes of cardiac origin that do not respond to conventional antiarrhythmic therapy
- •Recognition of this condition in horses may allow for targeted diagnostic and therapeutic approaches previously unavailable in equine medicine
Key Findings
- •Accessory pathways causing orthodromic atrioventricular reentry tachycardia have been documented in horses for the first time, previously only reported in humans and small animals
- •Retrograde conducting accessory pathways can create reentry circuits mediating both bradycardia and tachycardia through ventriculo-atrial conduction
- •Anterograde conduction along accessory pathways results in ventricular preexcitation bypassing the normal AV node-His-Purkinje system